1. Field of the Invention
The present invention relates to a conversion plug for an optical or light signal configured such that it can be plugged in directly an optical signal input terminal or optical signal output terminal mounted on one of various types of audio visual apparatuses or devices, personal computers, etc., and a method of fabricating the conversion plug, and more particularly, to a conversion plug for an optical or light signal comprising a plug portion adapted to be plugged in directly the optical signal input or output terminal and a plug-in hole for an optical plug that cannot be plugged in directly the optical signal input or output terminal, and capable of optically coupling between the optical plug inserted into the plug-in hole and the optical signal input or output terminal with low optical loss, and a method of fabricating such conversion plug.
2. Description of the Related Art
In recent years, with the advance of optoelectronics, there have been provided many kinds of audio visual apparatuses such as a DVD (Digital Versatile Disk) player/recorder, MD (Mini-Disk) player/recorder, CD (Compact Disk) player/recorder and the like, and electronic apparatuses or devices such as personal computers and the like, each being provided with an optical input terminal and/or optical output terminal for an optical or light digital signal (hereinafter, referred to as optical signal terminal). In an optical signal terminal is directly plugged one of two optical plugs mounted to an optical cable (for example, optical fiber) at opposed ends thereof respectively, that transmits an optical or light digital signal, thereby to transmit an optical digital signal from the optical signal terminal to the optical cable or from the optical cable to the optical signal terminal.
In Japan, there have been generally used as optical connectors for a digital audio signal an optical plug having its plug portion of 3.5 mm in outside diameter and an optical signal terminal (optical receptacle or jack) configured such that an optical plug of this size can be plugged in, and an optical plug having its plug portion of 2.5 mm in outside diameter and an optical signal terminal (optical receptacle or jack) configured such that an optical plug of this size can be plugged in. In addition, there are two types of optical plugs one being called a round or circular shape optical plug and the other being called a square or quadrilateral shape optical plug from the external appearances of their plug portions. The round shape optical plug can be plugged in only an optical signal terminal having its structure corresponding to that optical plug, and likewise, the square shape optical plug can be plugged in only an optical signal terminal having its structure corresponding to that optical plug. Though a square shape optical plug is configured that its core, namely, optical fiber projecting therefrom has a rod-like shape that is circular in section, a wall member of polygonal or square shape in section is coaxially formed about the core, and hence it will be called a square or quadrilateral shape plug.
As a result, it is impossible to plug a round shape optical plug having its plug portion of 3.5 mm in outside diameter in an optical signal terminal configured such that a round shape optical plug having its plug portion of 2.5 mm in outside diameter, for example, can be plugged in, and it is also impossible to plug a round shape optical plug having its plug portion of 2.5 mm in outside diameter in an optical signal terminal configured such that a round shape optical plug having its plug portion of 3.5 mm in outside diameter can be plugged in. The same is true in case of square shape optical plugs. In addition, even if two optical plugs have their plug portions of the same outside diameter, it is impossible to plug a round shape optical plug in an optical signal terminal configured such that a square shape optical plug can be plugged in, and it is also impossible to plug a square shape optical plug in an optical signal terminal configured such that a round shape optical plug can be plugged in.
For the reason described above, as is disclosed in Japanese Patent Application Public Disclosure No. hei 5-88043 (88043/1993), for example, there has been proposed an optical adapter that is capable of connecting two optical plugs having their plug portions of different outside diameters with each other. This optical adapter comprises a cylindrical adapter housing and an optical fiber of a predetermined length aligned on the central axis of the adapter housing, and optically couples, through the optical fiber aligned on the central axis of the adapter housing, between two optical plugs having their plug portions of different outside diameters plugged in the adapter housing from the opposed end portions thereof, respectively. If such type of optical adapter is used, it is possible to optically connect, for example, between a round shape optical plug having its plug portion of 3.5 mm in outside diameter and a round shape optical plug having its plug portion of 2.5 mm in outside diameter, between a round shape optical plug having its plug portion of 3.5 mm in outside diameter and a square shape optical plug having its plug portion of 2.5 mm in outside diameter, between a square shape optical plug having its plug portion of 3.5 mm in outside diameter and a round shape optical plug having its plug portion of 2.5 mm in outside diameter, or between a square shape optical plug having its plug portion of 3.5 mm in outside diameter and a square shape optical plug having its plug portion of 2.5 mm in outside diameter, with each other.
As described above, an optical plug is mounted to each end of an optical cable (an optical fiber is typically used as an optical cable, and hence it will be referred to as optical fiber, hereinafter), and one plug of the optical fiber is plugged in an optical signal terminal mounted on one of electronic apparatuses or devices or the like and the other plug thereof is plugged in the optical adapter. Since two optical plugs are inserted into the optical adapter, an optical coupling is effected between the optical fiber of the one optical plug inserted thereinto and the optical fiber provided in the optical adapter and between the optical fiber of the other optical plug inserted thereinto and the optical fiber provided in the optical adapter. In this manner, optical couplings inevitably occur twice in the optical adapter of such type, and hence there is an serious disadvantage that optical loss is increased. Moreover, two optical fibers are optically connected in series with each other through the optical adapter, and if the two optical fibers have the same length, the total length of the two optical fibers becomes twice the length of one optical fiber. It is preferred that the length of an optical fiber is as short as possible for the reason of optical transmission characteristic thereof.
For the aforesaid reasons, there has been earnestly desired in this technical field a conversion plug for an optical signal adapted to optically couple an optical plug that cannot be plugged in directly a desired optical signal terminal to this desired optical signal terminal with low optical loss and without lengthening the total length of the optical fiber.
In the technical field of electrical connectors, there has been put to practical use as disclosed in, for example, Japanese Utility Model Application Publication No. hei 1-29751 (29751/1989) an adapter-plug adapted to be capable of electrically connecting an electric plug that cannot be plugged in directly a receptacle or jack mounted on one of audio visual apparatuses or devices, and electronic apparatuses or devices such as personal computers and the like because the plug portion thereof has a different outside diameter, to that receptacle or jack. Such adapter-plug for an electrical signal is constructed such that it electrically connects an electric plug inserted into the adapter-plug with the adapter-plug with each other by use of electric contact pieces. Therefore, there is no technical concept at all in the adapter-plug for an electrical signal that it optically couple an electric plug inserted into the adapter-plug with the adapter-plug.
An object of the present invention is to provide a conversion plug for an optical signal adapted to be capable of optically coupling an optical plug that cannot be plugged in directly a desired optical signal terminal to this desired optical signal terminal with low optical loss.
Another object of the present invention is to provide a conversion plug for an optical signal that is low in optical loss, is easy in fabrication, and is inexpensive.
Further object of the present invention is to provide a method of fabricating easily a conversion plug for an optical signal that is low in optical loss.
In order to accomplish the foregoing objects, in one aspect of the present invention, there is provided a conversion plug for an optical signal which comprises: a plug portion to be inserted into directly an optical signal terminal of a specified size and having an optical fiber inserted thereinto; and a plug-in hole into which an optical plug having a plug portion that cannot be inserted into directly the optical signal terminal of a specified size can be inserted.
In a preferred embodiment, the aforesaid optical fiber to be inserted into the plug portion of the conversion plug has an optical fiber fixing ring previously joined with the optical fiber on the periphery of one end portion of the optical fiber, the end surface of the optical fiber protruding from the optical fiber fixing ring having been finished in mirror surface. The optical fiber fixing ring and the optical fiber are inserted into the conversion plug, and the optical fiber fixing ring is tightly fitted into the inside of the conversion plug to fix the position of the end surface of the optical fiber already finished in mirror surface.
The aforesaid conversion plug comprises: a ferrule constituted by a cylindrical sleeve portion having a fistulous tip portion at the forward end thereof, and a fistulous base portion formed integrally with the sleeve portion and having its outside dimension larger than that of the sleeve portion; and a fistulous optical plug supporting member to be tightly fitted into the inside of the fistulous base portion of the ferrule. The plug portion of the conversion plug is constituted by the tip portion and the sleeve portion of the ferrule, and the optical fiber is inserted into a through hole formed in the sleeve portion and the tip portion from the inside of the fistulous base portion of the ferrule as the optical fiber fixing ring is tightly fitted into the inside of the fistulous base portion of the ferrule. The plug-in hole of the conversion plug is formed in the fistulous optical plug supporting member.
In addition, the aforesaid conversion plug further includes an engagement spring to be inserted into inside of the fistulous base portion of the ferrule in such manner that it is in contact with the forward end of the fistulous optical plug supporting member, and elastically engaging and holding a tip portion of the plug portion of an optical plug to be inserted into the plug-in hole of the fistulous optical plug supporting member. The conversion plug further includes: a member made of an insulator that covers an peripheral area extending from the vicinity of the forward end portion of the sleeve portion of the ferrule to the vicinity of the forward end of the fistulous base portion of the ferrule; and a handle portion made of an insulator that covers the periphery of the fistulous base portion of the ferrule as well as the periphery of the fistulous optical plug supporting member except the backward end portion thereof.
The plug portion of the conversion plug may have its outside diameter which is the same as that of the plug portion of a round shape optical plug that can be inserted into directly the optical signal terminal of a specified size, and the plug-in hole of the conversion plug may be formed such that a round shape optical plug having a plug portion different in the outside diameter thereof from that of the plug portion of the conversion plug can be inserted thereinto.
Alternatively, the plug portion of the conversion plug may have its outside diameter which is the same as that of the plug portion of a round shape optical plug that can be inserted into directly the optical signal terminal of a specified size, and the plug-in hole of the conversion plug may be formed such that a plug portion of a square shape optical plug can be inserted thereinto.
Alternatively, the plug portion of the conversion plug may be formed to have the same shape as that of a plug portion of a square shape optical plug that can be inserted into directly the optical signal terminal of a specified size, and the plug-in hole of the conversion plug may be formed such that a plug portion of a round shape optical plug can be inserted thereinto.
Alternatively, the plug portion of the conversion plug may be formed to have the same shape as that of a plug portion of a first square shape optical plug that can be inserted into directly the optical signal terminal of a specified size, and the plug-in hole of the conversion plug may be formed such that a plug portion of a second square shape optical plug having a different size from that of the first square shape optical plug can be inserted thereinto.
In another aspect of the present invention, there is provided a method of fabricating a conversion plug for an optical signal which comprises the steps of: joining an optical fiber fixing ring and an optical fiber with each other to unify them; finishing the end surface of the optical fiber protruding from the optical fiber fixing ring in mirror surface; inserting the unified optical fiber fixing ring and optical fiber into the inside of a ferrule on which a member made of an insulator is mounted, and tightly fitting the optical fiber fixing ring further into the inside of the ferrule to fix the position of the end surface of the optical fiber already finished in mirror surface at the optimal position; inserting an engagement spring into the inside of the ferrule; and tightly fitting a fistulous optical plug supporting member having a plug-in hole into which an optical plug of a specified size can be inserted, into the inside of the ferrule.
In a preferred embodiment, the aforesaid method further includes, prior to the steps of inserting an engagement spring into the inside of the ferrule and tightly fitting a fistulous optical plug supporting member into the inside of the ferrule, a step of previously getting an amount for the optical fiber fixing ring to be tightly fitted into the inside of the ferrule using a jig.
In addition, the optical fiber fixing ring is tightly fitted into the inside of the ferrule in accordance with the tightly fitted amount previously gotten to fix the position of the end surface of the optical fiber already finished in mirror surface at the optimal position.
The aforesaid method further includes a step of forming a handle portion made of an insulator that covers the periphery of a predetermined portion of the ferrule as well as the periphery of the fistulous optical plug supporting member except the backward end portion thereof.
The aforesaid method may include a step of forming a protective cap for covering the tip portion of the ferrule and a protective cap for closing the plug-in hole of the fistulous optical plug supporting member integrally with the handle portion.
In accordance with the present invention, after the optical fiber fixing ring and the optical fiber have been joined integrally with each other, the end surface of the optical fiber is previously finished in mirror surface. As a result, the mirror surface finishing process is easily performed, one of various types of mirror surface finishing processes may be used, and the finishing state of the end surface of the optical fiber is easily confirmed. Moreover, since the end surface already finished in mirror surface of the optical fiber is protected in the periphery of the end surface by the optical fiber fixing ring, it is possible to insert the optical fiber into the ferrule, to correctly position, and to fix the optical fiber without causing damage on the end surface already finished in mirror surface.
Furthermore, by finely adjusting the position of the optical fiber fixing ring that has been tightly or closely fitted into the ferrule, the position of the end surface of the optical fiber can be fixed at the optimal position. As a result, even if there is any unevenness in the mirror surface finishing process for the end surface of the optical fiber or there is used a different mirror surface finishing method, the position of the end surface of the optical fiber already finished in mirror surface can be always set to the optimal position.